Geological Society of America

T134 New Advances in Geobiology

Monday, 16 October 2023
1:30 PM - 5:30 PM
325

NEW GEOCHRONOLOGICAL, GEOCHEMICAL, AND PALEOENVIRONMENTAL CONSTRAINTS ON THE TONIAN EUKARYOTIC MICROFOSSIL ASSEMBLAGE IN THE CHICHKAN FORMATION IN THE MALYI (LESSER) KARATAU, KAZAKHSTAN

Paper number: T134-6
Program: Technical Sessions
Time: 2:45 PM – 3:00 PM

Authors

Emily Smith Presenting Author
Johns Hopkins University, Baltimore, MD
Mary C. Lonsdale
Johns Hopkins University, Baltimore, MD
Lyle L. Nelson
Carleton University, Ottawa, ON
Dawid Szymanowski
Princeton University, Princeton, NJ
Dawid Szymanowski
ETH, 8092 Zurich
Sezim Mustapayeva
Satbayev University, Almaty, Almaty
Uyanga Bold
Mongolian University of Science and Technology, Ulaanbaatar
Kelsey Moore
Johns Hopkins University, Baltimore, MD
Cecilia Sanders
Johns Hopkins University, Baltimore, MD
Blair Schoene
Princeton University Geosciences, Princeton, NJ

Abstract

Major diversification within the eukaryotic clade is observed from the Tonian fossil record, but the drivers behind it remain unresolved, in part due to ambiguity surrounding the temporal and paleoenvironmental contexts of many Tonian microfossil assemblages. Here, we present new geochronological, geochemical, and sedimentological data from a vase-shaped microfossil (VSM)-bearing fossil assemblage preserved within the Malokaroy Series of the Malyi (Lesser) Karatau in Kazakhstan. We present U-Pb zircon geochronology and geochemistry of a volcanic unit within the Kurgan Formation, which overlies the Chichkan microfossil assemblage. T/REE data from the Tonian magmatic zircons suggest crystallization from magmas of rift or intraplate affinity. Based on these T/REE data, occurrences of pervasive fabric-retentive diagenetic chert within the strata, and abundant intercalated volcanic and volcaniclastic horizons, we suggest that early silicification contributing to microfossil preservation within these units resulted from localized syn-depositional to early-diagenetic sourcing of volcanogenic and/or hydrothermal silica. This model, in addition to the broader stratigraphic architecture of the basin, suggest that this Tonian ecosystem existed within a restricted basin rather than on an open, shallow marine shelf. Geochronology results indicate that the Chichkan Formation preserves one of the oldest VSM communities globally.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-391753

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